Home Secretary Amber Rudd said to give the police all the support they needed, the Government was supporting them in Operation Temperer so they could have Armed Forces assistance in order to “free up police”.

Speaking on Radio 4’s Today programme, she said: “They will basically be backfilling where police are otherwise occupied now, where they can do more work on this or on keeping people safe…”

She added: “This is a temporary arrangement in order to respond to an exceptional event.”

Troops will act as armed guards at Downing Street, the Palace of Westminster and foreign embassies, Scotland Yard said this morning

The Prime Minister Theresa May said she did not want the public to feel “unduly alarmed” but said it was a “proportionate and sensible response”.

And that “Military personnel may also be seen at other events over the coming weeks, such as concerts, working under the command of police officers…”

The Changing of the Guard ceremony in London has also been cancelled today, the Houses of Parliament are closed to non-pass holders and tours have been stopped indefinitely.

A statement on the Parliament website said:

“In light of the tragic events in Manchester and the Prime Minister’s announcement raising the national security threat level to critical, the police have advised that the Palace of Westminster should be closed to non-pass holders today, Wednesday 24 May”.

Chelsea football team have cancelled Sunday’s planned victory parade following security advice in the wake of the Manchester terror attack.

Operation Temperer was enacted following a meeting of the Government’s emergency Cobra committee at the request of the police after experts at the Joint Terrorism Analysis Centre (JTAC) raised the threat level from ‘severe’ to the highest ‘critical’ setting.

The threat level has only been raised to ‘critical’ twice since the system was introduced on August 1, 2006.

People have been sharing their views on twitter.

The Army got us through the Olympics – London 2012 – they'll do us proud now too #OpTemperer